1. Field of the Invention
The present invention relates to a 3GPP UMTS system and, more particularly, to a method for controlling a power of a shared control channel for high speed downlink shared channel (HS-SCCH) in a system adopting a high speed downlink packet access (HSDPA) technique.
2. Description of the Background Art
In general, a standard system of a third generation partnership project (3GPP) proposes a new high speed downlink shared channel (HS-DSCH) in order to support a high speed packet data service. The HS-DSCH is used in a UMTS system for Release 5 which specifies a high speed downlink packet access (HSDPA).
Unlike a W-CDMA system in 3GPP technical specifications for Release 99/Release 4, the HS-DSCH uses a short transmission time interval (TTI) (3 slot, 2 ms) and supports diverse modulation code sets (MCS) in order to support a high data rate.
Thus, an optimal data transmission performance can be improved by selecting the most suitable MCS for a radio channel condition, for which a hybrid ARQ (HARQ) technique is adopted which combines an automatic repeat request (ARQ) technique and a channel coding technique.
The HS-DSCH transmits high speed user data to different users for every sub-frame of 2 msec. Accordingly, in order for a terminal to receive the user data over the HS-DSCH, a shared control channel for HS-DSCH (HS-SCCH) and a dedicated physical channel (DPCH) should be configured.
The HS-SCCH, a physical channel, is a type of a downlink common control channel for supporting the HSDPA technique. The channel is used to transmit a UE ID (User Equipment Identification) and control information, whereby the terminal can receive the HS-DSCH transmitting the high speed user data. The terminal monitors the UE ID transmitted over the HS-SCCH to recognize whether there is data the terminal is to receive, and then, if there is data the terminal is to receive, receives the user data transmitted over the HS-DSCH by using the control information received from the HS-SCCH. Furthermore, the UE ID and the control information are transmitted for every sub-frame (2 ms) of the HS-SCCH. A Node B (a base station) to which a cell transmitting the HS-DSCH belongs generates the control information transmitted over the HS-SCCH.
FIG. 1 is a structure of a sub-frame of the control information transmitted over the HS-SCCH.
As shown in FIG. 1, the control information is roughly classified into transport format and resource related information (TFRI) and HARQ related information. The TFRI includes information related to a transport channel set size, modulation, a coding rate and the number of multicodes for HS-DSCH, and the HARQ related information includes information such as a block number and a redundancy version. Besides, UE ID is transmitted over HS-SCCH.
FIG. 3 is a drawing illustrating a transmission timing of the HS-SCCH and the HS-DSCH.
As shown in FIG. 3, after the UE ID and the control information are transmitted over the HS-SCCH, a data is transmitted over the HS-DSCH.
One or more HS-SCCHs are configured in one cell. In particular, if there are many UEs supporting the HSDPA technique in a cell, multiple HS-SCCH channels should be configured in one cell so as to efficiently provide data services.
In the conventional techniques, the common control channel is transmitted with a power level so high as to be received at a cell boundary.
However, in the case that the HS-SCCH is transmitted with such a high power as in the conventional techniques, an inter-cell interference is increased, and since a large amount of the Node B power (base station power) should be assigned for the transmission of the HS-SCCH, the Node B power is wasted
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.